The invention relates to a disk brake for a utility vehicle.
A generic disk brake is disclosed in DE 94 22 342 U1. Said disk brake has a brake lever which, during a braking operation, acts on a bridge in which at least one actuating spindle is mounted in a relatively rotatable manner. Said actuating spindle has a thrust piece which, during actuation of the brake, is pressed against a brake pad as a result of displacement of the bridge.
For the compensation of a wear-induced change of a predetermined air gap, that is to say of the distance between the brake pad and the brake disk, a readjustment device is provided by means of which the actuating spindle is adjusted in the direction of the brake disk by relative rotation. For this purpose, the actuating spindle is equipped with an external thread which engages into a corresponding threaded bore of the bridge.
A receiving space of the brake caliper in which the bridge and the brake lever are positioned is closed off to the outside, that is to say towards the brake disk, by a closure plate through which the actuating spindle extends.
To seal off said passage region, a corrugated bellows is provided which is held at one side on the closure plate and at the other side on the thrust piece. Said corrugated bellows is normally composed of a highly elastic material, for example a silicone rubber, in order that it can cover the actuating spindle over the entire readjustment travel. For the restoring movement of the bridge after a braking action, a compression spring is arranged between the closure plate and the bridge.
With regard to the durability, that is to say the service life, of the bellows, problems arise from the fact that the relatively high temperatures generated during braking operations act on the bellows, such that said bellows, as a wearing part, must be exchanged.
However, owing to the restricted space conditions, this is possible only with considerable expenditure of work, which considerably adversely affects the maintenance costs of the disk brake.
Aside from the expenditure of time, it is necessary, for the exchange of the bellows, for the actuating spindle to be rotated backward by means of the readjustment device, wherein, in order to protect the latter, during the resetting and feed movements, a breakaway adapter is used which breaks in the event of a particular torque being exceeded and thus protects a readjuster of the readjustment device against overloading. Furthermore, a disengagement prevention means is required for the readjustment device, because otherwise the actuating spindle becomes axially braced against the readjuster, which has the effect that a greater torque is required for a release than can be transmitted by the breakaway adapter.
DE 10 2008 010 462 A1 has disclosed a disk brake, the bridge of which has not a threaded bore but rather a blind bore in which a pressure plunger is mounted so as to be capable of performing tilting movements, wherein the pressure plunger is held in an axially secured but relatively rotatable manner in the bridge by means of a coupling ring which lies in circumferential grooves of the bridge, at one side, and of the pressure plunger, at the other side. Moreover, the pressure plunger is not equipped with a thrust piece which is rotatable relative to said pressure plunger, it rather being the case that the thrust piece is an integral constituent part of the pressure plunger. In this respect, said literature represents prior art of a different generic type.
The invention is based on the object of further developing a disk brake of the generic type such that it can be produced and assembled more easily and inexpensively, and exchange of wearing parts is made simpler.
The new disk brake is characterized firstly in that it can be produced much more easily than has hitherto been the case. This is contributed to in particular by the fact that the disengagement prevention means for the readjustment device, as mentioned with regard to the prior art, can be dispensed with, because a backward-rotation prevention means is realized by means of the securing ring provided according to the invention.
It is known from the prior art for a traction mechanism drive of the readjustment device, the actuating spindles, the bridge and the closure plate as main constituent parts to be introduced as a preassembled structural unit into the receiving space of the brake caliper.
For this purpose, it is necessary for the entire structural unit to be braced together. The axial securing of the securing ring on the thrust piece fixes said thrust piece in the axial direction, such that the closure plate is pressed by said compression spring against the thrust piece, which in turn pulls on the actuating spindle via the securing ring and thus, owing to the self-locking action of the thread, braces together the components of the unit that are involved. Thus, much simpler assembly of the disk brake, which takes less time, is possible.
In an advantageous refinement of the invention, it is provided that the securing ring, in order to be secured against relative rotation on the actuating spindle, is equipped with axially extending spring arms which engage into axial grooves of the actuating spindle.
For the installation of the securing ring, the latter is of resilient form and has a slot extending all the way through, such that, by being spread open, it can be guided over a head integrally formed on the actuating spindle, in particular during an exchange of the bellows and of the thrust piece. Here, after passing over the head of the actuating spindle, the securing ring is pressed together, for which purpose its outer diameter is smaller than the inner diameter of the thrust piece.
For the axial securing of the securing ring to the thrust piece, the securing ring has radially oriented tabs distributed over the circumference, which tabs engage into a circumferential inner groove of the thrust piece owing to the restoring forces of the resilient securing ring.
By means of the abovementioned relative-rotation prevention by means of the spring arms which engage into the axial grooves of the actuating spindle, the securing ring is rotated conjointly during the rotation of the actuating spindle. This permits a backward-rotation prevention action in interaction with the ring of a secondary seal of the bellows, which at one side is connected to the bridge, by frictionally locking fastening of the ring, and at the other side produces the frictionally locking connection of the bellows to the closure plate, wherein said bellows is connected to the ring of the secondary seal.
For the backward-rotation prevention action, lugs are provided on the securing ring on the side averted from the thrust piece, which lugs engage into cutouts of the ring in the event of the backward rotation of the actuating spindle.
Here, the webs formed between the cutouts are designed such that their width, converted by means of the transmission ratio of the thread of the actuating spindle, is jumped over in the case of an axial backward-rotation travel of for example 0.1 mm during the backward rotation. By contrast, the cutouts are of such a width that an axial backward-rotation travel of in this case 0.4 mm is covered. Here, it must be ensured that the securing ring is not axially braced with the ring of the secondary seal. This is achieved by virtue of the fact that the spring arms of the securing ring are designed to be resilient in an axial direction, such that the 0.1 mm axial backward-rotation travel required for the jump-over of a web of the ring is absorbed by the spring action.
As mentioned, in the region of the thrust piece and thus in the region of the securing ring, high temperatures act on the components involved during the operation of the brake. This poses particular challenges with regard to the spring steel in order to prevent the annealing thereof.
The advantage of the described construction lies in the fact that very small spring travels are required, owing to the transmission ratio of the thread pitch, normally M24-4P2, of 0.1 mm, in that the stresses occurring here in the securing ring lie below the Rp0.2 value of the base material, for example DIN EN 10132-4-C67S. Thus, an axial spring action is realized even in the annealed state of the securing ring.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.